Method of making a television screen



June 28, 1955 N. s. FREEDMAN EVAL 2,711,690

METHOD oF MAKING A TELEVISION SCREEN Filed June 1e, 1951 2 sheets-sheet 1 d 6s jffy 2, 3, f4 @7 4 j u Q ATTORNEY Jne 28, 1955 N. s. FREEDMAN ETAL METHOD oF MAKING A TELEVISION SCREEN 2 Sheets-Sheet 2 Filed June 16, 1951 /NvE/vmes Mrman Freedman IZZIUY osellil] ATTORNEY METHOD F MAKING A TELEVISION SCREEN Norman S. Freedman, Springfield, and Howard Rosenthal, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application June 16, 1951, Serial No. 231,978

2 Claims. (Cl. 101--129) This invention relates to cathode-ray tubes of the kind containing a dot-like or linelike beam-target and to irnprovements in the art of printing such targets.

The repetitive (dot or line) ray-sensitive patterns on the target plates of present-day tri-color television tubes are usually laid down, one color at a time, by the so-called silk screen printing process.

, As to the above see copending application of H. B. Law, Serial No. 158,901; now U. S. Patent 2,625,734. For an example of a color television dot" target-pattern see the copending application of A. N. Goldsmith, Serial No. 762,175; now U. S. Patent 2,630,542. See also Kasperowicz 2,508,267. Rudenberg 1,934,821 and the copending application of D. S. Bond, Serial No. 146,282, now U. S. Patent No. 2,689,926 show typical ray-sensitive line targets.

Unfortunately, repetitive-patterns printed by the silkscreen process, with presentday fabric-supported stencils, exhibit noticeably disturbing moir effects. The presence of moir in repetitive patterns printed with the aid of a conventional silk or metal fabricsupported stem cil, may be attributed to two facts:

f (I) Although the'apertures in the stencil are of duplicate form and dimensions, the ability of the different apertures to pass the printing ink is by no means iden* tical but is determined by the number and perhaps the relative position of the warp and weft strands that happen to span each aperture. As a consequence, the separate elements in the printed pattern, though of the same shape, may be, and usually are, of at least slightly different dimensions.

(Il) Because the stencil apertures used in printing repetitive patterns are equally spaced and since the strands of the supporting fabric are more or less equally spaced, the defects in the printed pattern tend to occur in groups which, in the eyes of the observer, comprise the waves and troughs of the watered-silk appearance which is characteristic of moire.

Accordingly, it is an object of the present invention to provide a reliable yet simple and inexpensive method of .and means for minimizing moir in the screen-printing of repetitive patterns, such, for example, as the raysensitive dot or line patterns heretofore used on the target surface of the viewing screens of some cathoderay tubes.

Another and important object of the invention is to provide an improved,colortelevision tube and one characterized (a) by its substantial freedom from moir effects,` (b) by the uniform brilliance of its colors and (c) by its high electron-optical resolution.

Stated generally, the foregoing and related objects are achieved in accordance with the present invention by the provision of a stencil wherein the lines or rows of openings through which the paint or ink passes are disposed at an angle with respect to the warp and weft strands of the metal (or silk) fabric upon which the stencil is supported. As will hereinafter more fully appear, this angle is different for different (dot or line) patterns.

2,? l l ,000 Patented .lime 28, 1955 Printing the pattern twice over, through dilerent stencilapertures, results in the optimum reduction in moir and, further, ensures uniform brilliance in the colors of the pattern without adversely affecting the resolving power of the sub-elementary color-areas on the finished ray-sensitive screen.

The invention is described in greater detail in connection with the accompanying two sheets of drawings,

wherein:

Fig. 1 is a broken away view in perspective showing a plate to be printed, and a portion of a printing screen comprising a fabric-supported stencil containing a repetitive dot-like pattern of apertures disposed at an acute angle with respect to the warp and weft strands of the fabric in the manner dictated by the present invention;

Fig. 2 is a View similar to Fig. 1 but showing a printing screen for the stenciled reproduction of a repetitive line-like pattern;

Fig. 3 is a longitudinal sectional view of a printing screen disposed above its initial printing position on a glass plate;

.Fig 4 is a View similar to Fig. 3 showing the printing screen removed from the second printing position dictated by the present invention and,

Fig. 5 is a broken away view in perspective of a color television tube of the maskedscreen variety, incorporating the invention.

In the drawings 1 designates generally the glass foundation plate of a television screen and 2 designates a gelatin, lacquer or similar stencil used in printing a repetitive ray-sensitive pattern on the target surface of said plate. The stencil is bonded to or otherwise supported upon a silk or metal gauze screen 3, which in turn, is supported upon a suitable wood or metal frame 4. The stencil shown in Fig. l contains a large number (say 2,000 per square inch) of circular holes 5 arranged in the repetitive hexagonal pattern used in the television screen of the Law application, Serial No. 158,901 (U. S. Patent 2,625,734). Here, as in the Law disclosure, the holes are spaced from each other a distance not less than the diameter of a single hole and are arranged in vertical and horizontal rows 5a and 5b, respectively, so that each hole (except the ones on the borders of the pattern) is surrounded by six other holes.

The present invention teaches that the moir effect normally present in repetitive patterns laid down (as on'the glass plate 1) by the sillt-screen7 process is minimized when the rows Sa and 5b of stencil apertures are disposed at an angle 0 with respect to the warp and weft strands 3a, 3b, respectively, of the fabric 3 upon which the stencil 2 `is supported. Where, as Fig. 1, the stencil apertures comprise discrete dot-like holes 5 the maximum reduction in the moir effect is achieved when the angle 0 is approximately 7. When the angle 0 is greater than 10 or less than 5, in the case of a dot-like repetitive pattern, the effect becomes increasingly noticeable to one observing the printed pattern.

In the embodiment of the invention shown in Fig. 2 the apertures in the stencil 2 comprise a multiplicity (say 1500) of equally spaced, parallel, line-like openings 5c, Which extend across the fabric screen 3 between opposite sides of the frame 4. This pattern of stencil apertures is useful in laying down ray-sensitive, line-like, target patterns similar to the ones shown in Fig. 2 of the Ruden'oerg patent (USP 1,934,821) and in the Bond disclosure (U. S. Patent 2,689,926). In this case the invention teaches that the maximum reduction in moir is achieved when the line-like stencil openings 5c form an angle (0) of 45, plus or minus, say, 2, with respect to the warp and weft strands 3a, 3b of the fabric 3 upon which the stencil 2 is supported.

Although mounting the stencil at the appropriateV angle (.9) with respect to the wrap and weft strands of its supporting fabric minimizes moir defects, the patterns printed through such a stencil may nevertheless exhibit certain other defects. By way of example, in the case of a phosphor dot or line screen the dots (or parts of the lines) may not all exhibit the same brilliance or the same optical resolution when illuminated by an electron-beam. Such defects may usually be traced either (a) to the presence of a warp or weft strand in a masking position, say adjacent to the periphery of one or more of the stencil apertures 5, as shown at x, x Fig. 1, or (b) to some defect in the stencil per se, such as the break shown at y Fig. 2.

The above described and similar defects may be repeated at lvarious points about the stencil, either symmetrically or non-symmetrically. The effects of such defects in the stencil Vare substantially eliminated, in accordance with the present invention, by the application of a second serving of phosphor (or other suitable ink) to the previously applied layer, through respectively different parts of the stencil. As indicated by the arrows in Figs. 3 and 4 this is done simply by shifting the position of the fabric-supported stencil 2-4-3 one or more dots (or lines) in any direction with respect to its position during the first printing and then applying the second printing through the stencil apertures with the screen in its new position. In re-printing a line pattern the stencil may be shifted in the direction of extension of the lines, instead of from one line to another. In either event, shifting the position of the screen prior to the second printing, brings a perfect stencil-aperture (5 Fig. 3) into register with the defectively printed phosphor element (6 Fig. 3) on the plate (l Fig. 3). Thus, when a second serving of phosphor is applied through the newly positioned screen said deflectively printed element or elements (6 Fig. 3) in the first printing are masked or overprinted by the second printing (as shown at 6a Fig. 4).

Phosphor dot and line screens, including tri-color screens, printed in accordance with the teachings of the present invention and illuminated by electron bombardment, are substantially free from moire effects and are further characterized by the brilliance of their colors and by their high electron-optical resolution. Fig. 5 shows such a tri-color dot-like screen `used as the ,target of a cathode-ray tube of the Goldsmith (U. S. Patent 2,630,542) masked-target" variety.

In Fig. 5 the screen, which is here designated 10, is provided on its rear or target surface with a multiplicity, say, 600,000. of phosphor dots 'R (red), B (blue), G (green) of different color-emissive characteristics. The dots are arranged in a hexagonal pattern in triads or groups-of-three (thus, each dot is surrounded by six other dots). The dots will be understood to have been laid down or printed, one color at a time, through the printing screen 2 3 of Fig. 1, said screen being-shifted between printings to a position whereat the stencil openings are tangent to the previously applied dots. (As 'to this see the vLaw patent, No. 2,625,734.) As in 'the Goldsmith disclosure (U. S. Patent 2,630,542), an apertured mask 11 is disposed in front of the target surface ofthe screen 10. The rnask 11 comprises a thin mtal plate containing 200,000 holes, i. e., one hole foreach of the tri-color dot groups.

The phosphor-dot screen and apertured mask 11 are here shown'mounted in the viewing chamber 12 of a kinescope 13 of the 3-g`un variety. The three guns which-are designated 15, 16 and 17 are mounted deltafashion about and along the central axis ofthe tube,in the manner disclosed in copending application Serial No. 166,416 of Hannah C. Moody. The paths of the electron-beams r, -16b and 17g converge in the 'plane of themask-ll where their paths cross and proceed in diverging straight lines to the screen 10. Thus, each beam irnpinges upon a different color dot. When different colorsignals are applied to the grids (not shown) of the different guns, and the signal modulated beams 15r, 16b and 17g are scanned over the surface of the mask 11, each beam produces a distinctively colored monochromatic image on the screen 10. These three distinctively colored images appear, to the eyes of the observer, as a single polychroniatic additive image, which, as previously set forth, is substantially free from moir and other defects characteristic of the mosaic type television screens ofthe prior art.

What is claimed is:

1. Method of making -a television-'beam target of the kind provided with a target surface having printed thereon a repetitive pattern consisting of rows of ray-sensitive areas, said method comprising; making a stencil with apertures disposed in rows corresponding to the desired pattern, mounting said stencil upon a fabric base with the warp and weft strands of said fabric disposed at an'a'ngle other than a right angle with respect to said rows of apertures, applying a rst serving of ray-sensitive material to discrete areas on said target 'surface through said fabric and stencil apertures, shifting said fabric supported stencil to a position whereat its apertures are in register with respectively different ones of said discrete ray-sensitive areas, and then applying a second serving of said ray-sensitive material to said areas through said apertures.

2. In the manufacture of a television-screen of the kind having a ray-sensitive target surface printed thereon in a repetitive pattern made-up of a multiplicity of uniformly disposed sub-elemental ray-sensitive areas; the method of minimizing screen-defects occassioned by the presence of non-repetitive defects in the printing element employed in laying down the ray-sensitive material on said target surface, said method comprising; applying said printing element to said screen to print said ray-sensitive repetitive pattern thereon, moving said printing element out of printing relationship with said screen and shifting said printing element relative to the printed pattern on said screen to a position whereat the sub-elemental areas of thepattern on said printing element are in register with different ones of the sub-elemental areas of said printed pattern, and then re-printing said printed pattern with said 'printing element'in its said registered position.

References Cited in the file of this patent UNITED STATES PATENTS 1,456,794 Gestetner May 29, 1923 2,209,499 Wulf July 30, 11940 y2,310,863 LCVECHZ Fb. 9, 1943 2,508,267 Kasperowicz May 16, Y'() 2,633,426 KOHCI Ml'. 31, :1953

FOREIGN PATENTS 497,194 Great Britain De'c. 412, "1938 

